U.S. patent application number 11/918919 was filed with the patent office on 2008-06-12 for separation method.
This patent application is currently assigned to WHITE FOX TECHNOLOGIES LIMITED. Invention is credited to Stephan Rudiger Blum.
Application Number | 20080135396 11/918919 |
Document ID | / |
Family ID | 36791774 |
Filed Date | 2008-06-12 |
United States Patent
Application |
20080135396 |
Kind Code |
A1 |
Blum; Stephan Rudiger |
June 12, 2008 |
Separation Method
Abstract
A feed stream is fed to a first distillation stage comprising at
least one distillation column (stripper) and the distillate from
the first distillation stage is fed to a second distillation column
(rectifier). The feed stream is sub-divided into two streams and
fed to two distillation columns, in such a way that the rectifier
maintains a predefined energy balance.
Inventors: |
Blum; Stephan Rudiger;
(Calgary, CA) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE
551 FIFTH AVENUE, SUITE 1210
NEW YORK
NY
10176
US
|
Assignee: |
WHITE FOX TECHNOLOGIES
LIMITED
South Kensington, London
GB
|
Family ID: |
36791774 |
Appl. No.: |
11/918919 |
Filed: |
April 19, 2006 |
PCT Filed: |
April 19, 2006 |
PCT NO: |
PCT/DE2006/000680 |
371 Date: |
December 21, 2007 |
Current U.S.
Class: |
203/25 ; 203/21;
203/27 |
Current CPC
Class: |
B01D 3/146 20130101;
B01D 3/143 20130101; B01D 3/004 20130101; B01D 3/148 20130101; Y02E
50/10 20130101; Y02E 50/17 20130101; B01D 3/322 20130101 |
Class at
Publication: |
203/25 ; 203/21;
203/27 |
International
Class: |
B01D 3/32 20060101
B01D003/32; B01D 3/14 20060101 B01D003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 2005 |
DE |
10 2005 018 508.8 |
Claims
1.-14. (canceled)
15. A process for separating an end product from a feed, the
process comprising: splitting a feed into two streams; sending at
least one of said streams to a first distillation stage comprising
at least one stripper; producing a distillate in the first
distillation stage; and sending the distillate from the first
distillation stage to a second distillation stage comprising a
rectification column, wherein the streams are processed so that the
rectification column maintains a defined energy balance.
16. The process of claim 15 wherein the two streams each have the
same energy.
17. The process of claim 15 wherein the two streams each have the
same chemical potential.
18. The process of claim 15 wherein the two streams have different
solids contents.
19. The process of claim 18 wherein one of said streams has no
solids.
20. The process of claim 15 wherein the two streams are at
different temperatures.
21. The process of claim 20 wherein one of the streams is in the
vapor phase.
22. The process of claim 15 wherein the two streams are sent to the
stripper and the rectification column, respectively.
23. The process of claim 15 wherein the two streams are sent to
respective first and second strippers in the first distillation
stage.
24. The process of claim 15 wherein the rectification column
produces a bottom product which is returned to the stripper.
25. The process of claim 15 further comprising: producing a
distillate in the rectification column; sending the distillate from
the rectification column to a filtration device; producing a
regenerate in the filtration device; and feeding the regenerate
back to the stripper.
26. The process of claim 23 further comprising: producing a bottom
product in the first stripper; and sending the bottom product from
the first stripper to the second stripper.
27. The process of claim 23 wherein the first stripper is run at a
higher pressure than the second stripper.
28. The process of claim 23 wherein the first stripper, the second
stripper, and the rectification column are operated at
progressively higher energies.
29. The process of claim 23 further comprising: recovering heat
from the end product; and feeding the recovered heat into a
reboiler circuit of the second stripper.
30. The process of claim 15 further comprising: recovering heat
from the end product; recovering excess energy obtained during
operation of the rectification column; and operating the first
distillation stage exclusively with the recovered heat and the
excess energy.
Description
[0001] The invention pertains to a separation process, especially
to the distillation of ethanol as an end product from a mash.
[0002] In a conventional process for the distillation and
dehydration of ethanol from a beer mash containing approximately
10% ethanol, 85% water, and 5% solids after fermentation, the mash
is preheated and sent to a first distillation column. In the first
distillation column, the mash is condensed by evaporation, as a
result of which solid components can be discharged as a bottom
product along with water. Some of this bottom product is usually
reheated and returned to the distillation column (reboiler).
[0003] The first distillate is in the form of vapor and still
contains water, ethanol, and fusel oils. It is sent, possibly by
way of a collecting and mixing tank, to a second distillation
column, which is designed as a rectification column. Further
separation occurs in this rectification column, during which the
fusel oils are discharged in a sidestream. A small portion of the
water precipitated out in the second distillation column as a
bottom product is reheated and returned to the rectification column
(reboiler) and also discharged, so that it is removed from the
production process. Some of the distillate of the second
distillation column, still containing water and ethanol, can be
returned to the first and second distillation columns, possibly by
way of the previously mentioned collecting tank. be returned to the
first and second distillation columns, possibly by way of the
previously mentioned collecting tank.
[0004] The predominant amount of the ethanol-water mixture
constituting the second distillate, consisting of approximately 95%
ethanol and 5% water, is subjected to a final dehydration to obtain
the purest possible ethanol with a purity of 99-99.8%. This last
dehydration step is carried out by means of molecular sieves, in
which crystalline zeolites, acting like sponges, adsorb the
H.sub.2O molecules.
[0005] The zeolites of a molecular sieve, however, rapidly become
saturated with water. So that uniform dehydration results can be
obtained, therefore, the water-saturated zeolites must be
regenerated. Molecular sieves are therefore normally used in pairs.
Thus highly pure ethanol can be obtained from a first, active
molecular sieve, and this ethanol can also be used to regenerate a
second, passive molecular sieve. When a passive molecular sieve is
regenerated, the ethanol being used can be returned to a
distillation column. This return stream can amount to approximately
30% of the pure ethanol obtained from the active molecular sieve.
The constant pressure swings to which the molecular sieves are
subjected lead to the formation of dust through the abrasion of the
filler material. This material collects in downstream stages of the
installation, which makes it necessary to replace these stages
completely at certain intervals. This has a disadvantageous effect
on investment and operating costs.
[0006] The dehydration of ethanol is an energy-intensive process.
In particular, the condensation of the mash in the first
distillation column as well as the need for large return flows of
distillate lead to considerable operating and investment costs.
Before the ethanol-water mixture can be treated with molecular
sieves, furthermore, the ethanol concentration must be
significantly increased to approximately 90-95%. For this purpose,
the substance mixture must be rectified as close as possible to the
azeotropic point, which requires a great deal of apparatus and
leads to considerable operating costs. The rectification column
must therefore have a large number of separation stages and a high
return flow rate.
[0007] It is known from PCT/DE2004/000867 that the energy
requirement of the rectification column can be decreased by
replacing the molecular sieves with membrane filtration units. As a
result of this measure, the distillate of the rectification column
needs to have a concentration of only 80 wt. % ethanol. The
required return flow is therefore much smaller than that necessary
for a process based on molecular sieves. The energy requirement of
the first distillation column, i.e., the stripper, remains
unchanged. Nevertheless, the overall energy balance is still not
satisfactory, because the rectification column is operating on a
lower energy level and therefore the amount of excess energy which
can be sent back from the rectification column to the first
distillation column is correspondingly smaller. The first column
must therefore be supplied with a considerable amount of outside
energy.
[0008] Against this technical background, the task of the invention
is to provide a separation process by means of which the economics
of the process can be improved, especially the economics of the
dehydration of ethanol from a mash.
[0009] To solve this technical problem, it is proposed for a
separation process, especially for the distillation of ethanol from
a mash, in which a feed is sent to a first distillation stage with
a distillation column, i.e., a stripper, and the distillate of the
first distillation stage is sent to a second distillation column,
i.e., a rectification column, that, according to Claim 1, the feed
be split into two streams and sent to two distillation columns in
such a way that the rectification column maintains a defined energy
balance.
[0010] The separation process according to the invention offers a
series of advantages. Previously, the energy concept of a
distillation plant was determined by the design of the stripper.
According to the invention, however, the first distillation stage
is operated on the basis of the energy input from the rectification
column, which can thus be operated under optimal conditions. The
energy balance of the rectification column thus essentially
determines that of the first distillation stage.
[0011] In a first variant of the process, the feed can simply be
split into two streams, so that both streams have similar energy
and/or chemical potentials. These streams are then each sent to a
distillation column. In most cases, the volume flow rate of the two
streams will also be approximately on the same order of magnitude,
each accounting for approximately half of the total, but, as a
function of the configuration of the first and second distillation
stages, it can also be effective in individual cases to split the
volume flow rates differently.
[0012] When the feed is split simply in this way, different volume
flow rates can occur when a first stream is sent to a stripper and
a second stream is sent to a rectification column. If provisions
are then also made to return a bottom product of the rectification
column, namely, the distillation column in the downstream position
with respect to the course of the process, to a stripper as the
upstream column, the energy balance per liter of end product
already becomes about 40% superior to that of conventional
processes.
[0013] Alternatively, if the feed is divided similarly into two
streams and if two strippers are provided in the first distillation
stage, one stream can be sent to each stripper, where preferably
the volume flow rates of the two streams will be approximately the
same. If then, in a preferred embodiment, it is also provided that
a bottom product of a first stripper, preferably operating at high
pressure, is sent to a second stripper, preferably operating at a
lower pressure, and if, in addition, the distillate of the
rectification column is purified in a membrane filtration device,
the energy balance improves by more than 60%.
[0014] In a further embodiment of the process of the invention,
separation devices such as screens, filters, membranes,
centrifuges, etc., can be used to obtain a higher concentration in
one of the feeds. When the feed is separated in this way into two
liquid phases of essentially the same energy level, it is possible
in a preferred variant of the process according to the invention to
send the retentate of, for example, a membrane separation device in
one stream to a stripper and to send the permeate in another stream
to a rectification column.
[0015] When a separation device is used, the feed is usually also
separated into a low-solids or even solids-free stream and a
high-solids stream.
[0016] If the feed is separated into two streams, one of which is
in the liquid phase and the other has an elevated temperature
and/or in particular is in the vapor phase, then this stream with
the elevated temperature, especially the retentate of, for example,
a membrane separation device, can be sent to a stripper, preferably
to the top of the stripper, and will be ready there to enter the
rectification column together with the distillate of this stripper.
The stream of lower temperature, e.g., the permeate, is fed into a
lower part of the stripper column.
[0017] In an elaboration of the previously described process, a
vapor phase-generating separation device such as an evaporator can
be provided, especially a device which generates a vapor phase by
expansion, or a distillation column can be used, the distillate of
which enters the rectification column along with the distillate of
a stripper, whereas its bottom product is sent to the stripper in
addition to another stream branched off from the feed.
[0018] Normally, the power requirement for the operation of the
first distillation stage will be completely covered by the excess
energy obtained from the operation of the rectification column and
from the recovery of heat from the end product. Thus optimal use is
made of the separation process according to the invention, because
the operation of the first distillation stage is determined
completely by the rectification column and the heat recovery from
the end product.
[0019] The distillation columns are preferably run at different
operating pressures, in particular at pressures which allow optimal
heat recovery. This guarantees the lowest possible heat loss.
[0020] This also makes it possible to operate three distillation
columns in a cascade configuration. Under the assumption that the
rectification column is operated at the highest energy level, a
stripper can be run on an intermediate energy level with the excess
energy obtained from the rectification column. With the excess
energy from the stripper column, preferably a second stripper can
then be run on a low energy level.
[0021] So that the energy level of the stripper operating on the
intermediate level can be kept as high as possible, it is
preferable for the heat recovered from the end product to be fed
into the reboiler circuit of the distillation column operated on
the intermediate energy level.
[0022] The amount of heat recovered from the end product can be
considerably increased if the concentration of the end product in
the feed is at least 20%. The energy input into the entire system
can then be considerably reduced in relation to the quantity of end
product obtained. Increasing the ethanol fraction in the feed by
about 10%, for example, can be achieved by means of an appropriate
fermentation technique. Alternatively, an upstream process such as
membrane separation, as previously mentioned, could be used to
increase the amount of end product in the feed. As a result of
these measures, the fraction of the end product in the overall
system increases considerably. These measures lead to a further
significant increase in the yield of end product and thus also to
an increase in the amount of heat recovered, which can be fed back
into the system.
[0023] In correspondence with conventional processes, the
distillate of the rectification column can be purified by molecular
sieves or preferably by membrane separation in a filtration device.
In particular, it is also possible for a regenerate of such a
filtration device located downstream from a rectification column to
be sent back to a stripper again.
[0024] The separation process according to the invention is
explained in greater detail on the basis of the drawing, which
illustrates the various sequences of process steps in schematic
fashion:
[0025] FIG. 1 shows three distillation columns and a final
purification stage using molecular sieves;
[0026] FIG. 2 shows an arrangement of three distillation columns
and a final purification stage consisting of a membrane separation
process;
[0027] FIG. 3 shows another arrangement of three distillation
columns;
[0028] FIG. 4 shows variants of how a regenerate can be fed to a
filtration device of a final purification stage;
[0029] FIG. 5 shows an arrangement of two distillation columns;
[0030] FIG. 6 shows a variant of how the feed can be split in the
case of two distillation columns;
[0031] FIG. 7 shows a splitting of the feed into preferably a
liquid and a vapor phase;
[0032] FIG. 8 shows a variant of the splitting into a liquid and
vapor phase;
[0033] FIG. 9 shows a splitting into a liquid and a vapor phase by
means of a distillation column; and
[0034] FIG. 10 shows a variant thereof.
[0035] In FIG. 1, two parallel-connected strippers 1, 2 form a
first distillation stage for a separation process, such as for the
distillation of ethanol from a beer mash. The feed 3, containing
approximately 11.5% ethanol, is split into two streams 40, 41 of
similar chemical and energy potentials and supplied to the two
strippers 1, 2 in equal amounts. The distillate 4 from the two
strippers 1, 2 is sent jointly to a rectification column 5. The
distillate 6 of that column is purified by molecular sieves 7 and
discharged as, for example, high-purity methanol with a purity of
99.6% as product stream 8.
[0036] According to the invention, the rectification column 5 can
be run at the highest energy level. For example, approximately
18,000 kW of primary energy 9 are supplied, indicated by the heat
exchanger in the reboiler circuit of the rectification column 5.
This includes an excess of approximately 9,800 kW, some of which,
as indicated, is fed via a heat exchanger 10 in the return line 12
of the rectification column 5 to the stripper 2, so that this can
be run on an intermediate energy level. Only approximately 8,500 kW
are required, however, for the operation of the stripper 2, which
means that approximately 1,300 kW can be taken unused from the
circuit, as indicated by the heat exchanger 11 in the return line
12.
[0037] The stripper 1 is operated with the excess energy from the
stripper 2. Approximately 6,500 kW are required for the first
stripper, which means that, if there is an excess of approximately
6,900 kW from the stripper 2, it is again possible to discharge
excess energy in the amount of approximately 400 kW.
[0038] Some of the excess energy can be used for the regeneration
and operation of the molecular sieves 7. There is still an energy
content of approximately 8,200 kW, however, in the distillate 6,
which is being sent with an ethanol purity of 93%, for example, to
the molecular sieves 7. It is true that some of this energy, i.e.,
approximately 3,000 kW, for example, is used for the operation of
the rectification column 5 by supplying the regenerate 13 of the
molecular sieves 7 or the like to the column, but approximately
5,200 kW ultimately still remains in the product stream 8. Because
of the way in which the molecular sieves 7 are operated, most of
this energy, e.g., about 5,000 kW, can be removed cyclically from
the system as unused heat, as indicated by the heat exchanger
14.
[0039] If the distillate is ethanol, a production rate of 19.57 L/h
can be achieved in this example at 1.58 kg of steam/L of
ethanol.
[0040] To ensure the cascade-like transfer of energy from one
distillation column to the next, the distillation columns 1, 2, 5
are run at different, graduated pressures. As a result, it is
possible for the distillation columns 1, 2, and 5 to operate in
optimal fashion with optimal energy transfer.
[0041] In the process according to FIG. 2, the molecular sieves are
replaced--a measure which has far-reaching consequences--by a
membrane filtration device 15. To operate this device in the case
of ethanol, the distillate 16 of the rectification column 17 needs
to have a purity of only 80%, for example. As a result, the primary
energy input needs to be only about 10,500 kW. The return 18 is
correspondingly lower in energy, and it thus provides only about
1,860 kW for the operation of the stripper 19. In corresponding
fashion, the distillate 16 has an energy content of approximately
8,600 kW. The two strippers 19, 20, however, are to be operated
essentially in accordance with the specifications of the preceding
exemplary embodiment.
[0042] The permeate 21 of the membrane filtration device 15
remaining in the process again makes available about 3,000 kW for
the operation of the rectification column 17. Therefore, about
5,600 kW remain in the product stream 22, of which about 5,000 kW
can still be used advantageously in a continuous manner, indicated
by a heat exchanger 23, for the operation of the stripper 19. Under
the assumed conditions, there remains a coverage gap of
approximately 1,660 kW, which must be supplied externally, as
indicated by the heat exchanger 24. Nevertheless, 1 liter of
ethanol is produced with 1.07 kg of steam for a product stream 22
of approximately 19.6 L/h.
[0043] In the process explained on the basis of FIG. 3, 20% of the
feed 25 consists of the end product, e.g., ethanol. As a result,
the quantity of distillate 26 of the two strippers 27, 28 is
considerably increased, whereas the energy demand is increased only
slightly and the working pressures remain unchanged. So that the
increased quantity of the distillate can be processed, the
rectification column 29 is operated at unchanged pressure with a
primary energy input 30 of approximately 14,500 kW, of which
approximately 2,500 kW is available in the return 31 for the
operation of the stripper 28.
[0044] The distillate 32 being supplied to a membrane filtration
device 33 has an energy content of approximately 12,500 kW at an
ethanol content of, for example, 80%. Feeding the permeate 34 back
to the rectification column 29 supplies about 4,700 kW. Thus about
7,800 kW remain in the product stream 35, which, as indicated by
the heat exchanger 36, can be fed back to the reboiler circuit 37
for the operation of the stripper 28; here, this stripper has an
energy requirement of about 9,700 kW, leaving an excess of 8,300 kW
for the operation of the stripper 27, which requires only about
8,050 kW. Sufficient energy is therefore made available to all the
strippers 27, 28, 29, which are connected to each other in an
energy cascade. In addition, the product stream 35 is considerably
increased to 30.46 L/h. This is obtained at an energy input of 0.83
kg of steam per liter of ethanol produced.
[0045] Variants are explained further on the basis of FIGS. 4-10,
which show simplified diagrams.
[0046] FIG. 4 shows two strippers 42, 43, which are supplied with
two similar streams 44, 45 of a feed 46. The distillate 47 of the
two strippers 42, 43 is sent to a rectification column 48, and the
distillate 39 of that column is sent to a filtration device 49.
[0047] In this exemplary embodiment, the regenerate 50 from the
filtration device 49, especially again a membrane filtration
device, is not fed back into the rectification column 48 but rather
into one of the strippers 42, 43, as indicated in broken line in
the drawing.
[0048] If desired, both strippers 42, 43 can be supplied with the
regenerate 50.
[0049] In the case of the exemplary embodiment according to FIG. 4,
the streams 44, 45 are of the same chemical and energy potential,
and each is introduced by way of example into an upper part of the
columns of the strippers 42, 43, whereas the distillate 47 of the
strippers 42, 43 is introduced more-or-less into the middle part of
the rectification column 48.
[0050] In the exemplary embodiment according to FIG. 5 with only
one stripper 51 and a rectification column 52, the two streams 53,
54 are fed into the stripper and the rectification column 52. In
this case, the volume flow rates of the two streams 53, 54 can also
be significantly different from each other.
[0051] The bottom product 55 of the rectification column 52 is not
discharged from the process but rather fed back to the stripper
51.
[0052] FIG. 6 shows the splitting of a feed 56 into two streams 57,
58 by means of a separation device 59. The separation device 59,
designed with screens, filters, membranes, centrifuges, or the
like, ensures, first, a significant increase in the fraction of the
end product, e.g., ethanol, in the stream 57 being supplied to a
stripper 60.
[0053] This stream 57 will then usually have not only an elevated
concentration of the end product but also a low solids content or
perhaps even no solids content at all.
[0054] In addition to a separation into two streams 57, 58 with
liquid phases and with essentially the same energy potentials, a
separation can also be carried out according to FIG. 7 by means of
a suitably designed separation device 61 into a first stream 62
with a temperature higher than that of a second stream 64. This
first stream can be in particular in the vapor phase and is sent
together with the distillate present at the top of a stripper 64 to
the rectification column 65. The second stream 64 is introduced
into a lower part of the stripper 63.
[0055] Suitably designed separating devices 61 can be evaporators,
for example, and in particular they can also be strippers 85 as
shown by way of example in FIG. 9.
[0056] FIG. 8 shows a variant in which a feed 66 is split into two
similar streams 67, 68. Stream 68 is sent directly to a stripper
86.
[0057] The other stream 67 is split again by a separating device 69
into two additional streams 70, 71. Stream 70 in particular is in
the vapor phase and is sent again together with the distillate
present at the top of the stripper 86 to the rectification column
87. The stream 71 can also be returned to the stripper 86 and thus
remain within the process.
[0058] In FIG. 9, a stripper 85 is provided as the separating
device (compare FIG. 8). Whereas the distillate 72 of the stripper
85 is of elevated temperature and is in particular in the vapor
phase and is sent together with the distillate present at the top
of a stripper 73 to the rectification column 88, the bottom product
74 of the stripper 85 is fed into the stripper 73.
[0059] The stripper 73 is also supplied with an additional stream
75, which has been branched off from the feed.
[0060] In the case of a process according to FIG. 9, it is
advisable for the distillation column 65 to be run at a pressure
higher than that of the stripper 73.
[0061] FIG. 10 shows how two strippers 79, 80 can be supplied by a
feed 76, which is split into two similar streams 77, 78. After
being combined as illustrated by way of example, the distillate 81
of those columns is sent to another distillation column 82. The
bottom product 83 of that column is then introduced into a
rectification column 84.
* * * * *